The invention relates to a belt tensioner for an auxiliary unit belt drive of an internal combustion engine with a tensioner housing, with a tensioner lever, and with a sliding bearing for the pivoting radial support of the tensioner lever in the tensioner housing, wherein a bearing partner associated with the tensioner lever is in sliding contact with a second bearing partner allocated to the tensioner housing.
From the prior art, such belt tensioners are known, e.g., these are also designated as self-aligning tensioners. Such self-aligning tensioners are alternatively also designated as self-aligning roller tensioners or ring tensioners. They are already known from the prior art in various constructions.
In this context, e.g., DE 10 2011 084 680 B3 discloses a tensioning device for a belt rive that has an endlessly revolving belt, an electric machine with a machine housing and a drive wheel and at least one other driving wheel that is in drive connection with the drive wheel via the belt. The tensioning device comprises a tensioner housing that is supported by a sliding bearing so that it can pivot about the axis of the drive wheel relative to the machine housing, two tensioning rollers that load the belt with pretensioning force in front of and behind the drive wheel in its direction of revolution, a spring that generates the pretensioning force, a tensioning arm that is supported against the force of the spring so that it can move in the tensioner housing, wherein one of the tensioning rollers is supported on the tensioning arm and the other tensioning roller is supported fixed in position on the tensioner housing, and a bearing carrier spans the tensioner housing in the axial direction.
Other prior art is known from EP 2 557 295 B1 and DE 10 2012 209 028 A1.
Noise-damped self-aligning bearings of decoupling tensioners can be used in critical start-stop drives that tend to generate noise due to, among other things, their layout by an unfavorable position of the resultant forces and associated low resultant radial forces on the self-aligning bearing and very high dynamic response that can result due to the lifting and dropping of one friction partner on the other. Typically, namely a base plate that is part of a tensioner lever is injection molded, wherein this injection molded end is held between a closing disk that is part of the tensioner housing and an adapter plate. The axial lengths are easily adjustable, but this is problematic in the radial direction. Under unfavorable conditions, this namely produces impacts or rattling in the radial direction. Adapter plates and closing disks are typically mounted stationary on the alternator, wherein the base plate is injection molded and connected rigidly to the housing and thus to the rest of the tensioner. An oscillating motion is provided. Under the already described circumstances, in the known systems, the resulting radial force on the self-aligning bearing can temporarily become zero or even reverse, which can lead to high-frequency lifting and impacting of the base plate on the closing disk. The injection molded part here impacts the closing disk. This can lead, in turn, to the generation of undesired noise.
Solutions have been put forward in which layout optimizations are performed in order to keep a resulting radial force on the pendulum bearing constantly greater than zero even for a counteracting dynamic response. However, this cannot always be implemented due to the installation space, customer requirements, etc. Changes to the corresponding tensioner parameters in order to reduce the dynamic response effect in order to, in turn, achieve a resultant radial force on the self-aligning bearing that is always greater than zero can also not be implemented in every tensioner design/drive.
The provision of an external pretensioning of the self-aligning bearing, in order to obtain a resultant radial force on the self-aligning bearing that is always greater than zero even for a counteracting dynamic response, e.g., through the use of a plate spring, would also be a conceivable solution that, however, would be considered disadvantageous for an O-ring as a damper with respect to weight, installation space, and costs. Minimizing the radial play in order to prevent lifting, despite the raised resultant radial force on the self-aligning bearing, does produce an improvement, but this cannot be implemented (in a cost neutral manner) in series production due to manufacturing, tolerance, and wear conditions.
Another complaint is that, in certain cases, it is not possible to design the tensioner or the drive so that in all operating cases viewed over the service life, the resultant radial force on the self-aligning bearing is greater than zero. For such drives, the noise can be prevented only by structural changes. A pretensioning of the self-aligning bearing, however, is not possible in a way that is neutral in terms of installation space, costs, and weight. Another possibility in addition to avoiding the cause, that is, preventing the lifting, would be an alternative approach.